John W. Farley

Observation of the visible absorption spectrum of H2O(

The A 2A1–X 2B1 system of H2O+ has been observed, using laser absorption spectroscopy in a velocity‐modulated discharge. A total of 78 transitions between 14 794 and 15 475 cm−1 have been observed with an uncertainty (1 SD) of 0.02 cm−1, including 76 transitions in the (0,7,0)–(0,0,0) band and 2 in the (0,8,0)–(0,0,0) band. This species is important for cometary astronomy, and intriguing for molecular physics because of its prominent Renner–Teller interaction. Careful measurements were made of the relative intensities of the absorption lines, which were measured to an accuracy of 13% (1 SD). This is the first observation of the A–X transition in absorption; all previous data were obtained in emission with conventional grating spectroscopy. The transition frequencies of our new data are in good agreement with previous work, and have improved accuracy. The new data have definite rejection of the interfering lines from excited neutral H2 that plagued previous work. Compared with previous work, the new ...

Theory of the resonance line shape in velocity‐modulation spectroscopy

Velocity‐modulation spectroscopy is often used to obtain absorption spectra of ions in discharges. However, there have been few studies of the line shape. The resonance line shape in velocity‐modulation spectroscopy is derived in the present work. Both sinusoidal modulation and square‐wave modulation are treated, and the differences in the resulting line shapes are emphasized. The results are relevant to measurements of ion mobilities, resolved with respect to the internal state of the ion.

Investigation of capillary electrophoresis-laser induced fluorescence as a tool in the characterization of sewage effluent for fluorescent acids: determination of salicylic acid.

The investigation of emerging contaminant issues is a proactive effort in environmental analysis. As a part of this effort, sewage effluent is of current analytical interest because of the presence of pharmaceuticals and their metabolites and personal care products. The environmental impact of these components is still under investigation but their constant perfusion into receiving waters and their potential effect on biota is of concern. This paper examines a tool for the characterization of sewage effluent using capillary electrophoresis‐laser induced fluorescence (CE‐LIF) with a frequency‐doubled laser operated in the ultraviolet (UV). Fluorescent acidic analytes are targeted because they present special problems for techniques such as gas chromatography‐mass spectrometry (GC‐MS) but are readily accessible to CE‐LIF. As an example of the application of this tool, salicylic acid is determined near the 100 ng/L (7 × 10–10 M) level in sewage effluent. Salicylic acid is a metabolite of various analgesics. Relatively stable in the environment, it is a common contaminant of municipal sewage systems. Salicylic acid was recovered from freshly collected samples of the effluent by liquid‐liquid extraction. Confirmation of identity was by electron ionization GC‐MS after conversion of the salicylic acid to the methyl ester by means of trimethylsilyldiazomethane. CE‐LIF in the UV has revealed more than 50 individual peaks in the extract and a background response that suggests a large and indeterminate number of additional compounds are present. These data together with complementary techniques provide information on the complexity and components in these effluent streams.

Double-modulation spectroscopy of molecular ions : eliminating the background in velocity-modulation spectroscopy

Velocity‐modulation spectroscopy is a well‐established technique for performing laser absorption spectroscopy of molecular ions in a discharge. However, such experiments are often plagued by a coherent background signal arising from emission from the discharge or from electronic pickup. Fluctuations in the background can obscure the desired signal. We demonstrate a simple technique using amplitude modulation of the laser and two lock‐in amplifiers in series to detect the signal. The background and background fluctuations are thereby eliminated, facilitating the detection of molecular ions.

The vibration-rotation spectrum of the ν1 band of nitroxide, HNO−

Abstract The infrared spectrum of the nitroxide ion, HNO−, has been recorded in the region between 2940 and 3150 cm−1 using high-resolution autodetachment detection spectroscopy. This wave-number range corresponds to absorption near the ν1 vibration, the NH stretching mode. The rR4, rR5, rR6, rR7, rR8, rR9, and rQ6 branches have been identified and rotationally analyzed, and rotational and centrifugal distortion constants for the (0, 0, 0) and (1, 0, 0) states have been obtained. The principal rotational constants, in cm−1, are A″ = 15.233360(380); (B″ + C″) 2 = 1.096829(24) ; (B″ - C″) 2 = 0.034424(900) ; A′ = 16.937355(280); (B′ + C′) 2 =1.088597(22) ; and (B′ - C′) 2 = 0.036066(1600) . The ν1 band origin is 2750.7827 (53) cm−1.

First observation of autodetachment lifetimes of methide, CH3−

The methide ion, CH3−, has been studied in a mass-selected ion beam. Two autodetachment lifetimes were observed that differ by three orders of magnitude. Infrared laser excitation near 3 micrometers reveals a vibrationally excited state with an autodetachment lifetime of 9–12 ns. This is the first resonant vibrational–rotational transition observed in methide. In addition, metastable ions were observed with a much longer autodetachment lifetime. For simplicity in the data analysis, all metastable ions are assumed to have a single autodetachment lifetime. This is an oversimplification, because the metastable ions decay by rotational autodetachment, and the metastable lifetime will therefore vary with rotational quantum number. The data analysis yields two possible values for the autodetachment lifetime: either 1.59±0.35 μs or 0.42±0.28 ms. The longer lifetime is much more plausible. The metastable states are attributed to rotationally excited states, which can only decay by channels with ΔJ⩾5. This interpr...

Ab initio study of nitroxide, HNO−

The first ab initio theoretical study has been performed on the ground state of nitroxide, HNO−, in combination with a comparison study of the ground state of two chemically similar systems, peroxy radical, HO2, and the neutral nitroxyl radical, HNO. An optimum geometry and vibrational frequencies are reported for all species, and results are compared to experimental and theoretical values. A bent geometry is obtained for HNO−, with an equilibrium bond angle of 106.2°, and bond lengths of RNO=1.333 A and RNH=1.045 A. The calculated fundamental vibrational frequencies (in cm−1) are: ν1 (N–H stretch), 3029; ν2 (bend), 1474; and ν3 (N–O stretch), 1183. The bending frequency and the N–O stretching frequency in the ion are similar to the bending frequency and the O–O stretching frequency of HO2, while the N–H stretching frequency of HNO− is similar to the N–H stretching frequency of HNO. In addition, the GAUSSIAN 1 and GAUSSIAN 2 methods are used for the determination of an electron affinity for HNO. The calcu...

Physics Metacognition Inventory Part II: Confirmatory Factor Analysis and Rasch Analysis

The Physics Metacognition Inventory was developed to measure physics students’ metacognition for problem solving. In one of our earlier studies, an exploratory factor analysis provided evidence of preliminary construct validity, revealing six components of students’ metacognition when solving physics problems including knowledge of cognition, planning, monitoring, evaluation, debugging, and information management. The college students’ scores on the inventory were found to be reliable and related to students’ physics motivation and physics grade. However, the results of the exploratory factor analysis indicated that the questionnaire could be revised to improve its construct validity. The goal of this study was to revise the questionnaire and establish its construct validity through a confirmatory factor analysis. In addition, a Rasch analysis was applied to the data to better understand the psychometric properties of the inventory and to further evaluate the construct validity. Results indicated that the final, revised inventory is a valid, reliable, and efficient tool for assessing student metacognition for physics problem solving.

Two-terawatt Zebra Z-pinch at the Nevada terawatt facility

A high-repetition-rate, 2-TW Z-pinch (Zebra or HDZP-II from LANL: 2 MV, 1.2 MA, 100 ns, 200 kJ, 1.9 ohm) has been assembled to investigate the early-time evolution of a current-driven wire, the plasma turbulence around and between wires, the acceleration of a plasma current sheet by a magnetic field, and the suppression or reduction of plasma instabilities, and to generate radiation for applications. The heating, expansion, and dynamics of wires driven by current prepulses similar to those at SNL-Z is being examined in isolated wires and soon in SNL-Z wire arrays. 290 trillion watts of X-rays can now be generated by a few cubic millimeters of plasma. The source of this plasma is the Z-pinch. This plasma confinement device drives a giant current through a tiny load, compressing and heating it with extreme current-produced magnetic fields. The Z-pinch suffers from plasma instabilities that limit its performance. The ultimate performance limit of the Z-pinch is unknown: another order of magnitude increase in X-ray power levels may be possible. Such an improvement would open up new applications. Understanding the dense Z-pinch is vital to the search to ameliorate it. This article describes the activation of the 2-TW Zebra Z-pinch, the development of diagnostics, and an initial single-wire experiment.

High-resolution laser spectroscopy of molecular ions

Laser spectroscopic investigations of positive and negative molecular ions are described. The experiments include studies of anions in an ion beam apparatus and of cations in a velocity- modulated discharge. In the coaxial beams apparatus, an infrared laser beam overlaps a 3 keV beam of molecular anions. The laser beam induces vibrational-rotational transitions in a negative ion. The vibrationally excited ion then autodetaches, producing a fast neutral. The neutral is then detected by collisional ejection of secondary electrons. This autodetachment technique has a background count rate near zero, and is, therefore, very sensitive. The transitions are sub-Doppler because of a velocity-bunching effect occurring in fast ion beams. Molecular anions whose vibrational-rotational spectra were measured include NH- and HNO-.